:: Ord a => [a] -> [a] -package:list-t -package:statistics -package:imports -package:witherable -package:ghc -package:extra -package:mono-traversable -package:safe -package:basement -is:exact -package:hxt -is:exact package:parsers
Take a parser that may consume input, and on failure, go back to where
we started and fail as if we didn't consume input.